Medical diagnostic ultrasound catheters include a shaft portion and a tip portion that surrounds an ultrasound transducer. Such catheters can be used for insertion into the arterial or venous system for imaging of blood flow or the heart. The tip portion of the ultrasound catheter is typically a homogeneous material that is selected for its acoustic properties. For example, a plastic that conducts ultrasound waves at a speed near that to the speed of sound in tissue or blood is often used. Although the material used for the tip portion may possess the desired acoustic characteristics, it may be relatively mechanically weak. For many catheters, though, the backing block material of the ultrasound transducer assembly aides in providing mechanical stability. However, when the diameter of a catheter is reduced, it is often necessary to thin the backing block material. For example, in moving from 10 French to 8 French, the backing block may be reduced from 30 mils to 20 mils. This reduction in the backing block reduces the mechanical stability of the catheter tip and can lead to de-lamination of the tip material from the transducer assembly. While using a tip material having greater mechanical strength avoids this problem, such a tip material may not provide desired acoustic properties.
There is a need, therefore, for a medical diagnostic ultrasound catheter that overcomes the problems described above.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims.
By way of introduction, the preferred embodiments described below provide a medical diagnostic ultrasound catheter with a tip portion carrying an ultrasound transducer. The tip portion comprises a first portion that is in the acoustic path of the ultrasound transducer, and a second portion that is outside the acoustic path of the ultrasound transducer. The first and second portions comprise different acoustic and mechanical properties. For example, the mechanical properties of the second portion can give the catheter tip sufficient durability to withstand normal use without bowing, while the acoustic properties of the first portion can give the catheter tip desired acoustic properties. This may be especially important for small diameter catheters (e.g., maximum cross-sectional dimensions less than or equal to about 10 French or 8 French) where the stiffness of the catheter tip is reduced.
The preferred embodiments will now be described with reference to the attached drawings.